The use of triazoles and particularly benzotriazole as an anti-corrosive or anti-tarnishing agent in various mediums, e.g. aqueous and organic mediums is well known. It has been found, however, that effective amounts of the carboxylated benzotriazoles including the alkali metal salts and aliphatic esters thereof have improved corrosion inhibiting characteristics and are superior to many of the other triazoles. Generally, this would not be expected since the introduction of a substituent (--COOH) to the benzene ring of benzotriazole increases its molecular weight and thereby lowers the relative proporton of the corrosion-inhibiting center, i.e. the triazole ring of the molecule. This would be expected to reduce the effectiveness of the corrosion-inhibiting properties of the molecule. To the contrary, it has been found that the carboxyl substituent on the benzene ring of the benzotriazole even though increasing the molecular weight of the compound improves its corrosion inhibition characteristics and in many instances is superior to the triazoles presently being used in aqueous and organic systems.
In general, corrosion is defined as a destructive attack on metal involving an electrochemical or chemical reaction of the metal with its environment. Specifically, an electrochemical attack on metal surfaces is the wearing away and under-cutting of the metal which is accelerated after the protective coating, e.g. the oxide film is removed by the corrosive medium, e.g. organic or aqueous mediums. In addition to electrochemical attack, other types of corrosion include cavitation and erosion where in addition to electrochemical reactions the conditions of the aqueous system are such that the continuous flow causes cavities where high pressure areas develop causing pressure shock resulting in a pitted metal surface. This type of corrosion generally is found in water pumps, propellers, turbine blades, etc. In addition, erosion of metal surfaces, generally occurs when the mediums, e.g. the aqueous liquid contains suspended solids which impinge the surface of the metal as the fluid is transported, e.g. through metal conduits or pipes, etc., removing the protective film causing exposure of the metal which is subject to further corrosion.